The invention relates particularly to machines capable of stretching in the longitudinal direction of the forming tool, i.e. in the direction perpendicular to its greatest curvature, requiring jaws that are so hinged as to enable them to pivot in compliance with the greatest curvature of the forming tool. The term "longitudinal stretching" is used below for referring to stretching as defined above relative to the positioning direction of the forming tool on the machine, and independently of the fact that the sheet metal may be stretched lengthwise or breadthwise. Conversely, the term "transverse stretching" is used when the sheet is stretched in the direction which corresponds to the greatest curvature of the forming tool.
Under such circumstances, the jaws are generally disposed rectilinearly.
In longitudinal stretching, there is a very wide variety of forming tools and the length thereof may be as much as 12 meters or as little as 50 cm, for example. In machines designed specially for transverse stretching, and having rectilinear clamps, the maximum width of the forming tool does not in general exceed 4 meters and a single table or work surface suffices for installing the tools.
However, for longitudinal stretching, the wide range of dimensions and the lightweight structure of the tools require tool carriers to be used that are of different dimensions.
However, the problem may also arise with machines for transverse stretching.
At present, two techniques are in use:
1/the first technique uses rigid modular tool carriers of dimensions such that each covers a range of tool formats. This solution makes it possible to support the tools over their entire length, but it requires the machine to be taken out of service for a long time when changing the tool carriers. It also requires very expensive and bulky handling and storage of said tool carriers, sometimes called "props"; PA1 2/the second known technique makes use of a plurality of tables: either two tables or three.
When using two tables, they are adjustable in spacing.
When using three tables, the middle table is fixed and the two side tables are adjustable in spacing relative to the middle table. This technique does not enable the forming tools to be fully supported and it therefore requires tools that are of reinforced structure, thereby increasing the cost and the weight of the tools. In addition, in this technique, there are deep gaps between the moving tables and these gaps must be covered by moving floors for essential safety reasons. The floors are put into place by hand.
An object of the present invention is to mitigate these drawbacks and to propose a structure that makes it possible to use forming tools that are lightweight in structure, that are fully supported, and that provide complete safety for personnel without requiring planks to be handled to cover any gaps. The principle of the invention is equally applicable to transverse stretching machines and to longitudinal stretching machines, and indeed the same machine may perform both ways if its clamps are capable of pivoting.